Usually, an elevator's drive sheave and motor are arranged above the elevator car in a machine room. In buildings, where space is at a premium, machine rooms are not desirable. Some elevators are powered by linear motors, which provide motive force for the elevator within a hoistway, and do not require a machine room.
Some linear motor driven elevators have a tubular primary element disposed around a tubular secondary element. The tubular secondary element is hung from the top of the hoistway. At present, it is impractical to hang a secondary element over an extended rise.
UK Patent Application 2,237,555 A to Toshiba shows another type of linear motor driven elevator which has a flat secondary and a flat primary element. The secondary element is affixed to the hoistway thereby avoiding the problem of hanging the secondary element from the top of the hoistway. The primary assembly of Toshiba is guided by the secondary thereby avoiding the necessity of mounting additional guide rails for the primary assembly.
Flat linear elevator motors balance the relatively large normal forces (as compared to thrust forces) between the primary and secondary elements to maintain an air gap therebetween. If the air gap is too great the motor is inefficient. If the air gap is too small, the motor may short itself out.